diff --git a/utils/src/format.h b/utils/src/format.h
index 27e467a5..b935d033 100644
--- a/utils/src/format.h
+++ b/utils/src/format.h
@@ -121,15 +121,9 @@ struct scoutfs_key_be {
 	__u8	_sk_fourth;
 }__packed;
 
-/*
- * Assert that we'll be able to represent all possible keys with 8 64bit
- * primary sort values.
- */
-#define SCOUTFS_BTREE_GREATEST_KEY_LEN 32
-/* level >0 segments can have a full key and some metadata */
-#define SCOUTFS_BTREE_MAX_KEY_LEN 320
-/* level 0 segments can have two full keys in the value :/ */
-#define SCOUTFS_BTREE_MAX_VAL_LEN 768
+/* chose reasonable max key and value lens that have room for some u64s */
+#define SCOUTFS_BTREE_MAX_KEY_LEN 40
+#define SCOUTFS_BTREE_MAX_VAL_LEN 64
 
 /*
  * The min number of free bytes we must leave in a parent as we descend
@@ -143,6 +137,14 @@ struct scoutfs_key_be {
 	 sizeof(struct scoutfs_btree_item) + SCOUTFS_BTREE_MAX_KEY_LEN +\
 	 sizeof(struct scoutfs_btree_ref))
 
+/*
+ * When debugging we can tune the splitting and merging thresholds to
+ * create much larger trees by having blocks with many fewer items.  We
+ * implement this by pretending the blocks are tiny.  They're still
+ * large enough for a handful of items.
+ */
+#define SCOUTFS_BTREE_TINY_BLOCK_SIZE	512
+
 /*
  * A 4EB test image measured a worst case height of 17.  This is plenty
  * generous.